Increasing injectivity by dilute alcohol injection

ABSTRACT

The effective permeability to water of a reservoir that contains residual oil near a well is improved by injecting a slug of an aqueous solution containing from about 6-20 percent of a normally liquid alcohol having a water solubility of from about 6-20 percent.

F'IPYQlZ.

United States Patent 1191' Abrams July 24, 1973 [541 INCREASINGlNJECTlVlTY BY DILUTE 3,288,215 11/1966 Townsend et a1 166/305 R ALC H LINJECTION 3,664,419" 5/1972 Holm 166/305 R X 3,064,732 11/1962 Bernardet a1. 166/305 R [75} Inventor: Albert Abrams, Houston. Tex. 3,236,3062/1966 Atwood 166/305 R 73 Assignee: Shell 011 Co., New York, N.Y. OTHERQ U N I "Handbook of Chemistry and Physics, 36th Ed., 1 Filed! J y 9,1971 1954-55, Chemical Rubber Publishing Co., Cleveland, [21] Appl. No.2161,341 Ohio, pp. 818, 819, 994 and 995.

, Primary Examiner-Stephen J. Novosad [52] U.S. Cl. 166/305 R, 166/273Ana-map", w Col-yell et aL [51] Int. Cl E211) 43/22,,E2lb 43/24 [58]Field of Search 57 ABSTRACT A 4 2 305 R; 252/855 B 1 The effectivepermeability to waterof a reservoir that {'56} R t k Cited containsresidual 011 near a \vell is improved inject- K 1 mg a slug of anaqueous solution contamlng from about UNITED STATES PATENTS 6-20 percentof. a normally liquid alcohol having a 3,467,188 9/1969 Gogarty .3.166/275 X water solubility of from abouti6-20- percent. 3,131,759 5/1964Slusser et al.....; 166/305 R 1 2,356,205 8/1944 Blair, Jr. t al.'166/305 R UX 6 Claims, N0 Drlwmgs 3,474,865

Gogarty'et a1l'. ,....l 1661275 x INCREASING INJECTIVITY BY DILUTEALCOHOL INJECTION BACKGROUND OF THE INVENTION This invention relates toa well treatment process for improving the effective permeability towater, (e.g., regarding water-injectivity) in a reservoir in which sucha permeability is restricted by the presence of residual oil in theregion near the well.

Previously proposed treatments for displacing such a residual oil awayfrom the near well region, and thus improving the injectivity, haveincluded the use of chemical flooding surfactant systems such as thoseused for fluid drive oil recovery processes, concentrated orsubstantially pure alcohols that are mutually miscible with oil andwater, etc. For example, U.S. Pat. No. 3,033,288 describes an oilrecovery process in which oil is displaced by injecting a slug of brineand then a slug of an alcohol that is relatively soluble in oil andwater but relatively insoluble in brine. U.S. Pat. No. 3,064,732describes a water injectivity improvement process in 'which oil isdisplaced by injecting substantially pure methyl alcohol. Suchpreviously proposed treatments tend to be relatively expensive due tothe cost of the mutually miscible solvents and/or the tailoring of thesurfactant systems and injection procedures. to the particularcharacteristics of the reservoir formation.

SUMMARY "OF THE INVENTION In accordance with this invention, theeffective permeability to water of a reservoir that contains residualoil near a well is improved by injecting a slug of a substantiallysurfactent-free aqueous saline solution containing from about'6-20percent by volume of a normally liquid alcohol having a water solubilityin said aqueous solution of from about 6-20 percent by volume throughthe well to displace residual oil away from the well.

The alcohol used may comprise one or more normally liquid alcohols ofthe specified water solubility. Such alcohols are preferably monohydric,aliphatic or alicyclic alcohols containing from about 3 to 6 carbonatoms. Illustrative examples of such alcohols include isopropyl alcohol,isobutyl alcohol, tertiary butyl alcohol, the pentanols, the aliphaticand alicyclic, hexanols and the like.

The aqueous liquid in which the alcohol is dissolved is preferably afresh water or a relatively soft water. Examples include fresh water,aqueous solutions containing from about 1 to 10 percent by weight of adissolved salt such as one or more alkali metal chlorides, bromides,sulfides, sulphates, nitrates, or the like. Aqueous liquids containingdissolved alkaline earth metal ions or anions such as sulphate anionswhich form insoluble salts with the alkaline earth metal ions can beused where they are compatible with the natural waters in the reservoirand/or aqeuous liquids previously injected into the reservoir.

The water solubility of the alcohol and the composition andconcentration of the salt dissolved in the aqueous liquid in which thealcohol is dissolved are preferably correlated so that the less solublealcohols are dissolved in the moredilute aqueous solutions of salts.

The amount of liquid (i.e., the slug of aqueous alcohol and, wheredesired, a subsequently injected slug of alcohol solution displacingfluid) injected in order to displace residual oil away from the wellbeing treated is preferably inclusive of at least about one pore volumeof the alcoholic solution relative to a cylindrical zone (co-extensivewith the vertical interval of reservoir'into which the well is opened)having a diameter of from about 5 to 10 feet. A preferred procedureutilizes at least about one pore volume of alcoholic solution relativeto a zone within the reservoir having a diameter of about 5 feetfollowed by at least an equal volume of an alcohol solution displacingfluid, such as fresh water or the aqueous liquid in which the alcohol isdissolved, that is miscible and unreactive with respect to the alcoholsolution.

In general, the aqueous alcohol should be injected at a rate that isrelatively high but is one that can be attained in response to aninjection pressure that is less than the fracturing pressure of thereservoir. A rate corresponding to a frontal advance of at least about 2to 4 feet per day (along a given radial direction away from the point ofinjection) is generally suitable. Particularly good results have beenattained by an injection rate corresponding to from about 50 to 60 feetper day.

[TEST RESULTS Short core apparatus and flow test techniques were usedfor all tests. Tests were conducted at F with cores confined in amodified Hassler holder under a simulated overburden pressure of 250psi. The floods were at constant rate. Pressure drop monitoring wascontinuous. Qualitative observations of the producing ratio of oil andwater were made during the floods. Flashed Wasson crude oil and aNujol-Soltrol mixture,

both with viscosity of 7.3 cp, were used as oil phases.

Solubility data were obtained by gas-liquid chromatography on isobutylalcohol-water solutions equilibrated at 105 F. This technique was usedalso to determine alcohol solubility in the oil mixture but could not beused for the crude oil because of the interference from components ofthe oil.

It can be seen from the data-presented in Table 1 that the addition ofthe alcohol increases the viscosities of the waters only slightly. Theinjection of these low viscosity treating agents could reduce thestability of the oil displacement stage but is compensated for by theease which the treating agents can be displaced by the follow-up water.

Distribution coefficients for Wasson injection water, 2 percent NaClsolution and 10 percent NaCl solution were determined by analyses of theoil and water phases in the swelling tests. They were found to be,respectively, 1.78, 1.63 and 2.27 for the Nujol-Soltrol mixture. Asmentioned earlier, we could not determine the amount of alcohol in thecrude oil but from data for the water phases, we conclude that thedistribution coefficients for the crude oil system are essentially thesame as those for the oil mixture. These coefficients indicate that weare dealing with an alcohol-rich oil phase which means that the oil canreadily extract alcohol from the injected alcohol-water solution.

Table 1 presents viscosity and solubility data and Tables 2, 3 and 4present results of flow tests.

TABLE I tion data are based on volumetric measurements initiated withthe water saturated core. Subsequent volumetric data are uncertainbecause of loss of control of oil volumes produced during the alcoholfloods due to solubimymercem 5 inadequate analytical procedures. Weestimated S System Dissolyeid I fl zm n oil saturation after chemicaldisplacement) by mea- ISCOSI Co I o o 555...) y in water alcohol surmgthe amount of 011 WhlCh could be in ected mto Waters I 700 0 64 the corefollowing an alcohol treatment. This was com- %2Sv0\;lalsl;: i l0i:mion910000 pared with initial oil and waterflood data to estimate g zj ggfilggfgf 20000 0 7O 10 the additional oil produced by the alcohol. Bythe same 0 N y %NaC1/di1sti11led water 3g,g8g 3.; 2 method we assuredourselves that the waterflood S 7 N C1 r d t Water s so iurz ngi w ithiszgiit i (resldualoilsaturation) value for a given core did not 084 89'7 change significantly. We include k (waterflood per- S l 90% Wass bninjection 10000 0 85 8 0 meabillty tn mrllldarcies) values at S,,,.obtained by wa- 107 Wasson produced m'jqacudismleg water fig ggg 8%.; 1415 terflood at 2-4 ft/day and at 50-60 ft/day. 57 NaCl/distille water y10 /distilled water 100.000 0.90 4. Of considerable importance is theeffect of rate on k,,, T at S,,,. Although the changes in saturationoccurring 8, ft p d d t t s on] flowtests damn during an increase inrate from 2-4 ft/day to 50-60 3550 "BBC IDII'PI'O CC W3 61" mlX ure W311 5B In r eluded to Show effects of salinity on alcohol solubility inwater. ft/day 18 of the order of 2-4 saturation percent, we

TABLE 2 RESULTS OF FLOW TESTS ON THE EFFECTIVENESS OF ISOBUTYL SATURATEDWITHISOBUTYL ALCOHOL IN ALCOHOL AND WATER SOLUTIONS INCREASING k AT SPermeuhilit -and saturation data (ore description Fluid systemswaterflood tests lnj-ctiutty improvement tests 1 w w 1c, at k... atS,,,, ik at i 5.... Sum k... (perm. "fl 0 100 S md S,,,. MD V, S.,.md Vm md (improv. k/kw (poeffec- Oil Water Injection 12-4 ft/day) 150-60ft/day) 150-60 ft/day) ratio) tential) tivcness) Indiana limestone cores0. =1 .6 md Nujol- Wasson ROH' 8.5 0.31 1.16 27 5 12.1 7.3 6.3-23.523.5-6.3 41 17.5% soltrol inj.

Nujol- Wasson W+ ROH 8.8 0.32 30 1.16 27 18 3.1 3.6 3.1-1 1.3 ll.3-3.120

soltrol inj. wzlsstdm W2SOn ROH 12.] 0.97 25 3.2 23 10 10.6 6.6 2.1636.192.] 38

cm e in Wasson Wasson W+ ROH 12.0 0.91 25 2.2 23 19 3.3 4.2 1.9-4.64.6-1.9 24

crude in. No. 6 it 86.5 md Wasson was son ROH 92. 6.8 18.2 32 5 63.443.4 2.4-6.4 6.4-2.4

da= 17.2% crude inj.

Wasson Wasson W+ ROH 85.9 8. 35 20.6 32 24 30.5 34.3 1.7-3.9 3. -1.7 40

crude in'. N0. IL I k=22.5 md Wasson Was son ROH 21.6 1.18 30 4.0 28 513.4 16.7 4.214.2 14.2-4.2 74

=15.2% crude inj.

Wasson Was-son W+ ROH 17.6 1.37 30 4.5 28 18 6.1 6.5 1.4-4.7 4.7-1.4 29

crude inj. Was-son 1A enver unit wel17504. Wasson Wasson ROH 12.7 1.5 303.6 Z8 15 1.5.4 1.1.6 3.8-9.1 9.1-3.8 100 4996-97 ft crude inj. Zone M-3k=12.2 md =l6.5%

Wasson Wassun W+ ROH 12.7 1.5 30 3.6 28 25 4.4 4.7 1.4-3.1 3.1-1.4 39

crude inj.

All cores except [L are l in. diameterX 2 in. length. 11. is 1 in.diameterX 8.4 in. length.

"S is oil saturation left by treatment. "k represents k at S.,,=100%;""ROH represents alcohol. W represents water phase.

Since wettability can affect waterflood saturations and permeabilities,we checked the wettability of the cores tested in this study and foundthem to be water- 7 k1., is the water penneability following treatment.

TABLE 3 EFFECT OF FLOW RATE ON k AT S Fluid systems k md. at indicatedflow rate, ft/day Core On Water 2-4 14-16 -27 26-38 -60 Indianalimestone No. 4 Nujol- Wasson 0.31 0.51 0.70 0.94 1.16

soltrol inj.

Wasson Wasson 0.91 1.33 1.67 2.2

crude inj.

(not measund) No. 6 Wasson Wasson 6.8 10.4 14.1 17.3 18.2

crude inj.

No. 11. Wasson Wasson 1.18 2.1 2.7 3.4 4.0

crude inj. 2.6 2.9 3.6 3.6 Wasson 1A Wasson Wasson 1.23 1.76 2.4 2.9 3.6

crude inj.

Initial waterfloods conducted at 2-4 ft/day. Water injection rates werethen increased incrementally to obtain values shown.

Arrows indicate direction of rate changes.

For increase in rates from 2-4 ft/day to 50-60 ft/day, AS. 5 24%.

TABLE 4 RESULTS OF FIIOW TESTS ON THE EFFECTIVENESS OEVARIOUS WATERSOLUTIONS SATURATED WITH ISOBUTYL ALCOHOL 1N INCREASING k AT S Indianalimestone" No. 4

stone core No. 4 and Wasson core'lA. However, for the other twocores,.the observed reduction in k as the rate is decreased suggeststhat part of the change in k,,, is due to redistribution of .thefluidsin the core as well as a change in average oil saturation.

Permeabilities to alcohol-water andalcohol alone, k',,,,, and waterpermeability followingtreatment, k' are included in Table 2. Increasesin k achieved with the treatment were determined by comparing k,.,, withthe water-flood k values (k' /k permeability improvement ratio in Table2). We seethatalcohol alone increasesthe low rate k values by factorsranging from about 7 to 25; the alcohol-water systems achieves factorsof about 3-17. Lesser 'increasesin k result from the high rate"waterflood. I

As shown earlier, the solubility of isobutyl alcohol in water decreases,with increasing salinity. We would anticipate that .these differencesinsolubilityshould be re- 7 I a? Permeability and saturation data l idsystems w fl d [e515 7 lnjectivity improvement tests 'w/ w i a! S kw imim-t k'itnu P (k'W/k) X 01 Water 1 It. a! s... md vv 5... ma v,, v,.k... imp ov. /k.v 6 1% effec- 4 md (24 ft day) (50-601l/day) (50-60t/dny) rnd ratio) tential) ttvenessl Nujol- Wasson ROH 8.5 0.31 30 1.1627 5 12.1 7.3 24-63 57-152 41 soltrol inj.

Wasson W+ROH 8.8 0.32 30 1.16 27 111 3.1 3.6 1 1.3-3.1 55-151 20 in v 2%W+ ROH 7.9 0.27 30 1.24 27 10-15 3.3 4.7 17.4-311 -142 27 5% W+ ROH, 7.50.29 30 1.26 27 10-15 3 4(4.6J* (5.9) 61-14.0 (34) 10% W+ ROH 8.7 0.3430 1.62 27 10-15 3.5 4.9 l4.4-3.0 5210.9 28 Wasson Wasson ROH 12.1 0.9725 3.2 23 10 10.6 6.6 6.8-2.1 l8.15.5 38

crude inj.

Wasson W+ ROH 12.0 0.91 25 2.2 23 19 3.3 4.2 4.6-1.9 19.3-81.0 24

111]. 2% W..+ ROH 12.0 0.97 25 2.9 23 10-15 3.6 4.6 4.7-1.6 l8.1-6.1 2610% W+ ROH 13.7 0.90 25 4.0 23 10-15 4.7 5.3 5.9-1.3 l9.64.4 30

Data enclosed by are based on treatment rate of ft/day.

flected in performance during treatment as well as in overalleffectiveness. To measure such effects, we conducted flow tests with thedifferent alcohol-water solutions listed in Table 4. Experimentally,weused'the' water that formed thealcohol-water system for waterfloodingthe test core prior to treatment and for' displacing the alcohol systemafter treatment. Changeover of waters was made atS Basedon pressureresponse, the flow 'tests showed alcohol-Wasson injection water thewaterin which the alcohol is most soluble. Response was almostimmediate. with the Wasson water; whereas the other waters showed lagsof 0.25 to 0.50 pore volume, the largest that mobilization of oiloccurred most rapidly with the traces for the 2 percent, 5 percent andpercent NaCl solutions are essentially superimposable when correctionsare made for difference in response time and fluid viscosities. Thealcohol-Wasson injection waterflood was completed after about 1 to 1.5pore volumes of injection whereas the other floods required about 3-5pore volumes. The delay in response is related to the extraction ofalcohol by the oil as the treating fluid enters the core. Larger volumesof water are required for the waters having a reduced alcoholsolubility. The pressure data behavior supports the S values reported inTable 4. The reduction in oil saturation for the higher salinity watersystems is larger than for the fresher water.

The results of flow tests using alcohol-water solutions in whichsalinity was varied, presented in Table 4, indicate that theeffectiveness of a treatment increases with salinity of the water phase.This effect is more pronounced with the Nasson crude oil than with theoil mixture. For both oils, the Wasson injection water system was lesseffective than the higher salinity fluids. The alcohol-water mixtureswere at least 5075 percent as effective as the alcohol alone. Includedin the table primarily to show trends in k values is a test withalcohol-5 percent NaCl as the treating agent in which the rate duringthe treatment was increased from 50-60 ft/day to over 150 ft/day. Theadditional increase in permeability was accompanied by the production oftraces of oil.

One of the difficulties in judging the value of a treatment forincreasing k by reducing S is the uncertainty of the water permeabilityin the formation. Laboratory tests on the effect of flow rate onwaterflood S and k show that variations in k of threefold can occur byincreasing the rate from 2-4 ft/day to 50-60 ft/day,

a range of rates of interest for injectivity in the formation. Our testsshow that isobutyl alcohol-water systems can displace enough oil toincrease k at S by factors of about 3-17 when compared to a low ratewaterflood k Similarly, increases varying by factors of about 1.3 to 3.8are calculated using high rate reference data.

What is claimed is:

1. A well treating process for improving the effective permeability towater by injecting an oil displacing fluid to displace residual oil awayfrom a well comprising:

injecting a substantially surfactant-free aqueous saline solutioncontaining from about 6 to 20 percent by volume of a normally liquidalcohol having a solubility in said aqueous solution of about 6.to 20percent by volume; and

injecting said aqueous solution at a rate providing a frontal advance offrom about 50 to feet per day along a radial direction away from thepoint of injection.

2. The process of claim 1 in which the aqueous solution of alcohol isdisplaced by a substantially alcoholfree aqueous liquid that is injectedat substantially the same rate as the aqueous solution of alcohol.

3. The process of claim 1 in which the aqueous solution in which thealcohol is dissolved contains at least about 1 percent by weightdissolved salt.

4. The process of claim 1 in which said alcohol is an aliphaticmonohydric alcohol that contains from about 3 to 6 carbon atoms.

5. The process of claim 1 in which said alcohol is isobutyl alcohol.

6. The process of claim 1 in which said alcohol is isopropyl alcohol.

2. The process of claim 1 in which the aqueous solution of alcohol isdisplaced by a substantially alcohol-free aqueous liquid that isinjected at substantially the same rate as the aqueous solution ofalcohol.
 3. The process of claim 1 in which the aqueous solution inwhich the alcohol is dissolved contains at least about 1 percent byweight dissolved salt.
 4. The process of claim 1 in which said alcoholis an aliphatic monohydric alcohol that contains from about 3 to 6carbon atoms.
 5. The process of claim 1 in which said alcohol isisobutyl alcohol.
 6. The process of claim 1 in which said alcohol isisopropyl alcohol.